Conventionally, as a flow rate control valve using a diaphragm, there is the flow rate control valve described in Japanese Patent Application Laid-Open No. 2010-159790 (Patent Document 1). In the flow rate control valve in Patent Document 1, a diaphragm pressing surface of a diaphragm spacer is made such that a central part located more inward than a tip diameter of an annular valve seat is formed as a plane surface or a gently curved surface, and a peripheral edge part located more outward than the tip diameter of the annular valve seat is formed as a tapered surface that is more recessed than a virtual surface where the central part has been extended. The annular valve seat is of a shape that its leading end part is made as a flat surface and it has tapered surfaces on the outer peripheral side and the inner peripheral side bordering on the flat surface, and has a structure that the diaphragm abuts against the flat surface of the annular valve seat leading end part by pressing force of the diaphragm spacer.